At present, a discharge type fluorescent lamp and an incandescent bulb used as an illumination device involve problems that a harmful substance such as mercury is contained, and life span is short. However, in recent years, an LED emitting light of near ultraviolet/ultraviolet to blue color has been developed in sequence, and study and development have been actively performed to obtain an illumination device of the next generation capable of emitting light of white color by combining the light of ultra violet to blue color generated from this LED and the phosphor having an excitation band in the wavelength range from the ultraviolet to blue color. This illumination device has a lot of advantages such as less heat generation, with good life span without burn-out of a filament like an incandescent bulb, because it is constituted of a semiconductor element (LED) and a phosphor, and a harmful substance such as mercury is not contained, thus realizing an ideal illumination device.
Here, in order to obtain white light by combining the aforementioned LED and the phosphor, generally two systems can be considered. As one of them, the LED emitting blue color and the phosphor emitting yellow color that receives this blue emission and excited by this blue light, are combined, and white emission is obtained by combination of the blue emission and yellow emission which are set in a complementary color relation.
As the other one, the LED emitting near ultra violet and ultraviolet, the phosphor emitting red color (R) under excitation by emission of the near ultraviolet and ultraviolet, the phosphor emitting green color (G), the phosphor emitting blue color (B), and the phosphor emitting other color, are combined, to obtain white emission by mixture of the lights of these R, G, B, etc. By a method of obtaining the white emission by means of the light of these RGB, etc, an arbitrary emission color other than the white light can be obtained by combination and mixing ratio of the phosphors that emit light of the RGB, etc, and therefore an application range as the illumination device is wide.
As the phosphor used in this purpose of use, Y2O2S:Eu, La2O2S:Eu, 3.5MgO.0.5MgF2.GeO2:Mn, (La, Mn, Sm)2O2S.Ga2O3:Eu are given as examples of the red phosphor, ZnS:Cu, Al, CaGa2S4;Eu, SrGa2S4:Eu, BaGa2S4:Eu, SrAl2O4:Eu, BAM:Eu, Mn, (Ba, Sr, Ca)2SiO4:Eu are given as examples of the green phosphor, and BAM:Eu, Sr5(PO4)3Cl:Eu, ZnS:Ag, (Sr, Ca, Ba, Mg)10(PO4)6Cl2:Eu are given as examples of the blue phosphor. Then, by combining the phosphor emitting these RGB, etc, and a light emission part (light emitting element) such as the LED emitting light of the near ultra violet and ultraviolet, a light source such as the LED emitting white light or a desired monochromatic light, and an illumination device including this light source can be obtained.
However, in the illumination obtaining white color by combining a blue LED and a yellow phosphor (YAG:Ce), the light emission on the longer wavelength side of a visible light region is insufficient, resulting in the emission of slightly bluish white color. Therefore, slightly reddish white emission like an electric bulb can not be obtained.
In the illumination of obtaining white color by combining the near ultra violet/ultra violet LED and the phosphor emitting light of RGB, etc, an excitation efficiency of the red phosphor out of three-color phosphors is deteriorated on the longer/wavelength side, thus deteriorating the emission efficiency. Therefore, a mixing ratio of the red phosphor must be increased, and in this case, the phosphor for improving luminance is insufficient, thus making it impossible to obtain a high luminance white color.
Therefore, in recent years, a oxynitride glass phosphor (for example, see patent document 1) having an excellent excitation on the longer wavelength side and capable of obtaining an emission peak with a broad half value width, the phosphor with sialon as a matrix (for example see patent documents 2, 3, 4), and the phosphor containing nitrogen such as silicon nitride-based nitrogen (for example, see patent documents 5, 6), are proposed. These phosphors containing nitrogen have a larger ratio of covalent bond, compared with an oxide-based phosphor, and therefore have an excellent excitation band even in the light of the wavelength of 400 nm or more, and are focused as the phosphor for the illumination device emitting white light.
Also, inventors of the present invention also reports the phosphor having a broad emission spectrum in a range of red color, having a broad flat excitation band in the range of the near ultraviolet/ultraviolet, and having an excellent emission efficiency. (see patent documents 7, 8, 9).    Patent document 1: Japanese Patent Laid Open Publication No. 2001-214162    Patent document 2: Japanese Patent Laid Open Publication No. 2003-336059    Patent document 3; Japanese Patent Laid Open Publication No. 2003-124527    Patent document 4: Japanese Patent Laid Open Publication No. 2004-067837    Patent document 5: Published Japanese Translation of a PCT Application No. 2003-515655    Patent document 6: Japanese Patent Laid Open Publication No. 2003-277746    Patent document 7: Japanese Patent Laid Open Publication No. 2005-239985    Patent document 8: Japanese Patent Laid Open Publication No. 2006-008862    Patent document 9: Japanese Patent Laid Open Publication No. 2006-028295